1. Field of the Invention
This invention relates in general to fly height performance testing, and more particularly to a method and apparatus for precise measurement of pressure dependence of head fly height using transitional thermal signals.
2. Description of Related Art
Storage capacity governs the amount of data a user can store on a computer. Adding storage capacity without increasing size means denser radial spacing of tracks on disk drives. As a result, the read/write head element's magnetic sensitivity must also increase, which makes the manufacturing process even more demanding and acceptance testing more critical.
Conventional magnetic storage devices include a magnetic transducer or "head" suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force us counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides toward the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer's ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Some fly height stability is achieved with proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
Another important factor affecting fly height is the slider's resistance to changing conditions. An air bearing slider is subjected to a variety of changing external conditions during normal operation. Changing conditions affecting fly height include, for example, change in the relative air speed and direction, pressure changes and variations in temperature. If the transducer fly height does not stay constant during changing conditions, data transfer between the transducer and the recording medium may be adversely affected. Fly height is further affected by physical characteristics of the slider such as the shape of the ABS. Careful rail shaping, for example, will provide some resistance to changes in air flow. To insure compliance with such design criteria the recording heads are typically tested in an apparatus commonly referred to as a fly height tester.
Head fly height in a disk drive is dependent on the attitude at which the drive is functioning for a variety of slider air bearing designs. The head usually flies lower at higher attitude, i.e. lower pressure. Accurate measurement of head fly height vs. pressure is of importance for air bearing and file design optimization as well as for further understanding of head flying dynamics mechanism. However, the sensitivities of fly height testers have not provided accuracy at the sub-nanometer (nm) level, which is required to verify the compliance of today's head. Moreover, the pressure dependence of head fly height has not been measurable.
It can be seen that there is a need for a method and apparatus for precise measurement of pressure dependence of head fly height.